This invention relates to a device to retain heat that is normally lost from workpieces (i.e., forging billets) that have been preheated to an elevated temperature. For example, billets must be preheated to high temperatures for forging, or for other types of severe mechanical forming processes, so that they may be readily deformed. It is common practice in forging operations to preheat billets in "batch process" furnaces and to remove a billet to transport it to the forging die as operations at the die permit. Because the billet loses heat to its environment during transport to the forging die, it has been necessary to preheat to a higher temperature than is actually necessary for forging in order that the billet be at a suitable temperature at the time it reaches the die and throughout the forging operation.
In addition, such heat loss shortens the time available for the actual forging operation. For example, titanium generally cannot be forged once the temperature has dropped below 1400.degree. F., and steel generally cannot be forged below 1900.degree. F. Titanium is typically preheated to approximately 1800.degree. F. and steels to 2350.degree. F. to 2450.degree. F. to compensate for heat loss during transportation. During the typical one to two minute period required to transport a titanium billet to the die, the temperature typically will have dropped to about 1650.degree. F. The time for the temperature to drop to 1400.degree. F. will, of course, be much shorter than if the billet had arrived at the die at 1800.degree. F. This shortening of the time during which forging operations can be undertaken on the billet can be quite expensive in terms of reduced production capacity. Thus, if forging cannot be completed in the short time available (typically about five minutes), the billet must be reheated and forged again. Not only does this tie up equipment for a longer period of time before the desired product is achieved, but problems of quality control are also introduced.